A battery (a secondary battery) deteriorates at a speed corresponding to a usage environment. With the deterioration, an amount of charge at a full charge decreases and discharge characteristics deteriorate. Deterioration of a battery mounted on a vehicle causes deterioration of a running performance. Therefore, it is preferable that a time period capable of providing a predetermined performance for the battery is estimated in advance. A technique in JP2007-195312A estimates a battery deterioration degree associating with a square root of a total running distance to predict a residual life.
However, the method of JP2007-195312A estimating the battery deterioration degree on the basis of the square root of the total running distance has a problem where an estimation error is large.